RLV Reliability Analysis Guidelines

1. RLV Reliability Analysis Guidelines Terry Hardy AST-300/Systems Engineering and Training Division October 26, 2004

2. Introduction • What are reliability analyses? • Why are reliability analyses important? • Why develop guidelines? • How are reliability analyses used? • Acceptable reliability analysis methods. • Typical documentation.

3. What Are Reliability Analyses? • Reliability analyses are quantitative and qualitative tools used to determine whether an item will perform its intended function for a specified interval under foreseeable operating conditions. • Reliability is not safety • Components may be reliable and still unsafe • Accidents arise from interactions between machines, software, humans, and the environment, as well as from component failure • Reliability must be considered in the context of system safety.

4. Why Are Reliability Analyses Important? Reliability analyses are important because: • Risk to the public can depend on reliability of safety-critical systems and consequences of failures of those systems. • Reliability analyses can provide risk assessment data to support launch vehicle safety analyses. • Reliability analyses help make decisions leading to improved reliability and safety.

5. Why Develop Guidelines? AST is developing Reliability Analyses Guidelines to: • Facilitate valid RLV reliability analyses by providing a set of acceptable methods that demonstrate compliance with regulatory requirements. • Provide examples of methods and approaches to assist RLV developers. • Capture best practices in the aerospace community. • Illustrate integration of safety and reliability analyses.

6. How Are Reliability Analyses Used? Reliability analyses can be used to: • Support the system safety process: • Identify potential reliability/safety problems • Compare alternate designs to improve reliability/safety • Identify operational/test requirements • Provide validation and verification data • Provide vehicle failure probability estimates to support Ec analysis. • Help specify operating restrictions. • Evaluate whether a flight safety system will meet reliability or safety requirements. Guidelines will document how reliability analyses are applied

7. Acceptable Reliability Analysis Methods • Reliability Block Diagrams • Parts Count Analysis • Failure Modes, Effects, and Criticality Analysis • Fault Tree Analysis • Event Tree Analysis • Reliability Allocation • Probabilistic Risk Assessment • Monte Carlo Simulation Guidelines will describe each of these methods, including approach, advantages, disadvantages, and RLV-specific examples

8. Typical Documentation Reliability analysis documentation typically includes: • Item identification • Intended use of the analysis results • Analysis methods used • Analysis inputs • Analysis results • Confidence in analysis (assumptions, sources of uncertainty, limitations) Guidelines will provide a description of each documentation element

9. Summary • AST is developing RLV Reliability Analysis Guidelines to facilitate valid reliability analysis. • Guidelines will include how reliability analyses are used, acceptable methods, and RLV-specific examples. • Draft guidelines posted for comment: April 2005